....I would still argue that it is rude to tie up any resource for an unusual amount of time, especially when you can choose to use a similar but not identical resource, but a segment of the population cannot make that same choice.
I would feel it was rude to spend a long time in a single toilet restroom as well if you could avoid it. Then you would be keeping all women (assuming you're using the women's room of course) from using the bathroom. I do tend to be more careful of how long I'm in one of those rooms. This isn't' different to me.
I understand where you're coming from, but I really feel like most women are eager to get in, take care of business, and get out again as soon as is humanly possible. At least, that's my feeling about public restrooms 
Sometimes, though, people have to occupy a stall for a while. I would be interested in knowing how you determine if someone's situation was avoidable?
I think the problem is that people are more likely to use that stall if they know they are going to take awhile. To give some examples of times I thought someone was being rude while using the stall:
1) A full change of clothes in the airport, plus full face makeup (she darted in there ahead of me so I know she put it on while in there).
2) Having a phone conversation in there (rude anyway in my opinion).
3) A full change of clothes when there were changing rooms right next to them in the locker room.
4) Not rude, but not nice was the person who was clearly having issues and darted in there ahead of me. She didn't need the stall for mobility issues (not an assumption, I knew her but she didn't know me), but I can understand wanting more room if you're not feeling well. On the other hand, it meant I needed to leave the building to use the bathroom. This is the one I feel could be arguable. She was using the stall for it's intended purpose, but she also took a resource one step "up" from what she needed, but I couldn't have used the other stalls.
Mrkitty, I fully understand that the law doesn't require people to refrain from using those stalls. I wouldn't even argue that etiquette requires people to not use the stalls ever. I have no issue waiting an appropriate amount of time. On the other hand, when was the last time you waited more than 5 minutes to use a bathroom? Because that happens much more frequently if there is only one bathroom you can use.